1. Nick Cooper, Stefan Renner Carl Murray Encelade Meeting, UPMC, 22 January 2014 Recent Results on the Dynamics of Atlas

2. Charnoz et al. (2010)

3. Astrometric Data 2580 Cassini ISS observations of Atlas, Prometheus, Pandora, Janus, Epimetheus QM SATELLORB and F Ring Images Data span Feb 2004 to Aug 2013 Atlas observations mostly centroided UCAC2 for pointing correction Phase correction SATELLORB astrometry by Mike Evans

4. Numerical Model Integration of full equations of motion in 3D Perturbations from 8 major satellites, Sun, Jupiter Saturn’s oblateness up to J6 Runge-Kutta-Nystrom 12 th order integrator Variational equations integrated simultaneously, iteratively fitting to observations Solving for states and masses of Atlas, Prometheus, Pandora, Janus and Epimetheus at epoch

5. Pre-fit (SAT353)Post-fit O-C Residuals

6. O-C Post-fit Residuals

8. Mean longitudes vs. time Resonant arguments vs. time ILR CER

9. Full Numerical Model Atlas, Prometheus, Saturn only Atlas Geometrical Elements

10. FLI vs time Full Numerical Model 3-body Numerical Model (Atlas, Prometheus, Saturn)

11. (Starting Conditions from Numerical Fit) Coralin Surfaces of Section ATLAS a_mean=137665.39 km

12. Coralin Surfaces of Section (Starting Conditions from 3-body Model) ATLAS a_mean=137665.39 km

13. Summary Fit to new astrometry: significant reduction in O-C residuals. Order of Magnitude improvement in mass estimates. Atlas dynamics dominated 54:53 resonance with Prometheus. Another example of coupled ILR/CER motion! Regular and chaotic episodes (FLI analysis). Chaos is due to Prometheus only. Atlas, Prometheus dynamics can be modelled as a 3-body system (CORALIN).